For example, I want to say that I found a ball today. But "today" means action in present, am I right?
I've already searched the Internet and it seems the right way is this:
I found a ball today
But it seems wrong when I say "today" and "found" (I'm not using words like "earlier"). Maybe it's right to say:
I have found a ball today
And why can't I say
I find a ball today
Which way is right and why?